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An OpenGL example with support for Linux/Unix/BSD and Emscripten.
/*
Build instructions:
To compile and run the application with G++ or Clang++ use:
$ CXX -o application.o -c opengl_emscripten_example.cpp
$ CXX -o application application.o -lGLEW -lGLU -lGL -lglfw
$ ./application
To compile and with Emscripten use:
$ em++ -o application.o -c opengl_emscripten_example.cpp -s MAX_WEBGL_VERSION=2
$ em++ -o application.html application.o -lGLEW -lGL -lglfw -s USE_GLFW=3
$ emrun --no_browser application.html
*/
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <iostream>
#ifdef __EMSCRIPTEN__
#include <emscripten.h>
GLFWwindow *glfwMainWindow;
GLuint mainShaderProgram;
GLuint globVertArrObj;
GLuint scalarID;
float scalar = 0.5f;
float scalarFactor = 0.00390625f;
#endif
const char *vertexShaderSource =
#ifndef __EMSCRIPTEN__
"#version 330\n"
"layout (location = 0) in vec3 aPos;\n"
"uniform float scalar;\n"
"void main()\n"
"{\n"
" gl_Position = vec4(scalar * aPos, 1.0f);\n"
"}\0";
#else
"attribute vec3 aPos;\n"
"uniform float scalar;\n"
"void main()\n"
"{\n"
" gl_Position = vec4(scalar * aPos, 1.0);\n"
"}\0";
#endif
const char *fragmentShaderSource =
#ifndef __EMSCRIPTEN__
"#version 330\n"
"out vec4 FragColor;\n"
"void main()\n"
"{\n"
" FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n"
"}\0";
#else
"void main()\n"
"{\n"
" gl_FragColor = vec4(1.0, 0.5, 0.2, 1.0);\n"
"}\0";
#endif
void framebuffer_size_callback(GLFWwindow *window, int width, int height);
void processInput(GLFWwindow *window);
// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;
#ifdef __EMSCRIPTEN__
void glfwIter()
{
// scale the triangle
if (scalar == 1.0f)
{
scalarFactor = -0.00390625f;
}
if (scalar == 0.5f)
{
scalarFactor = 0.00390625f;
}
scalar += scalarFactor;
glUniform1f(scalarID, scalar);
// input
// -----
processInput(glfwMainWindow);
// render
// ------
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(mainShaderProgram);
glBindVertexArray(globVertArrObj);
glDrawArrays(GL_TRIANGLES, 0, 3);
// glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
// -------------------------------------------------------------------------------
glfwSwapBuffers(glfwMainWindow);
glfwPollEvents();
}
#endif
int main()
{
// glfw: initialize and configure
// ------------------------------
if (!glfwInit())
{
std::cerr << "Failed to initialize GLFW" << std::endl;
return -1;
}
// glfwWindowHint(GLFW_SAMPLES, 4);
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
// glfw window creation
// --------------------
GLFWwindow *window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "OpenGL Example", NULL, NULL);
if (window == NULL)
{
std::cout << "Failed to create GLFW window" << std::endl;
glfwTerminate();
return -1;
}
glfwMakeContextCurrent(window);
glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
// initialise GLEW
glewExperimental = true;
if (glewInit() != GLEW_OK)
{
std::cerr << "Failed to initialize GLEW" << std::endl;
glfwTerminate();
return -1;
}
// vertex array object
GLuint vertArrObj;
glGenVertexArrays(1, &vertArrObj);
glBindVertexArray(vertArrObj);
// triangle vertices
float triangleVertices[] = {
-0.5f, -0.5f, 0.0f, //
0.5f, -0.5f, 0.0f, //
0.0f, 0.5f, 0.0f //
};
GLuint triangleVertBuf;
glGenBuffers(1, &triangleVertBuf);
glBindBuffer(GL_ARRAY_BUFFER, triangleVertBuf);
glBufferData(GL_ARRAY_BUFFER, sizeof(triangleVertices), triangleVertices, GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void *)0);
glEnableVertexAttribArray(0);
// triangle shaders
GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
glCompileShader(vertexShader);
int success;
char info_log[512];
glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
if (!success)
{
glGetShaderInfoLog(vertexShader, 512, NULL, info_log);
std::cout << "Error while compiling vertex shader: " << info_log << std::endl;
return -1;
}
GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
glCompileShader(fragmentShader);
glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
if (!success)
{
glGetShaderInfoLog(fragmentShader, 512, NULL, info_log);
std::cout << "Error while compiling fragment shader: " << info_log << std::endl;
return -1;
}
GLuint shaderProgram = glCreateProgram();
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
glLinkProgram(shaderProgram);
glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
if (!success)
{
glGetProgramInfoLog(shaderProgram, 512, NULL, info_log);
std::cout << "Error while linking shader: " << info_log << std::endl;
return -1;
}
glDeleteShader(vertexShader);
glDeleteShader(fragmentShader);
// render loop
// -----------
#ifndef __EMSCRIPTEN__
float scalar = 0.5f;
float scalarFactor;
GLuint scalarID = glGetUniformLocation(shaderProgram, "scalar");
while (!glfwWindowShouldClose(window))
{
// scale the triangle
if (scalar == 1.0f)
{
scalarFactor = -0.00390625f;
}
if (scalar == 0.5f)
{
scalarFactor = 0.00390625f;
}
scalar += scalarFactor;
glUniform1f(scalarID, scalar);
// input
// -----
processInput(window);
// render
// ------
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(shaderProgram);
glBindVertexArray(vertArrObj);
glDrawArrays(GL_TRIANGLES, 0, 3);
// glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
// -------------------------------------------------------------------------------
glfwSwapBuffers(window);
glfwPollEvents();
}
#else
glfwMainWindow = window;
mainShaderProgram = shaderProgram;
globVertArrObj = vertArrObj;
scalarID = glGetUniformLocation(shaderProgram, "scalar");
emscripten_set_main_loop(glfwIter, 60, 1);
#endif
// glfw: terminate, clearing all previously allocated GLFW resources.
// ------------------------------------------------------------------
glfwTerminate();
return 0;
}
// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
void processInput(GLFWwindow *window)
{
if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
glfwSetWindowShouldClose(window, true);
}
// glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow *window, int width, int height)
{
// make sure the viewport matches the new window dimensions; note that width and
// height will be significantly larger than specified on retina displays.
glViewport(0, 0, width, height);
}
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